Bug when decreasing toc from h3 to h1 for example

[barais]

scully-plugin-toc/projects/scully-plugin-toc/src/lib/toc.ts

Line 94 in c3b7afc

toc += '</ul>';

In this line, it could be better to change it for managing if we have such kind of outline

h1

h2

h3

h3

h1

for (let j = 0; j< previousTag - level ; j++ ){
    toc += '</ul>';
}